Knitting Trials & Tribulations

Currently, the big project on my needles is an afghan for my future sister-in-law.  It's sort of my own design, but the layout and some of the cabling elements come from the Burridge Lake Afghan (link is for Ravelry if you are a knitter).  I wanted something a little less busy than the Burridge Lake Afghan and I didn't like all of the cables in it and definitely not the Trinity Stitch.  So, I did some research and picked some cables I liked, figured out which would work well together in terms of repeats, decided on the cables, figured out the spacing I wanted and came up with my pattern.  Like the Burridge Lake Afghan, I am knitting this in panels.  I'm nearly done with the first panel - just trying to decide if it is long enough.  Should it be just a lap afghan or should it be long enough that FSIL and cover herself head - well shoulder - to toe with it?  If I want the latter - do I have enough yarn.  So last night I was doing math.  One ball of yarn is getting me about 118 rows.  At that rate, I will need just over 3 balls to complete the first panel.  Since the third panel is the same series of cables - just left to right instead of right to left - the third panel should take the same amount of yarn.  The center panel is double the width of the others - in stitches anyway - so theoretically it should be double in terms of yarn usage.  So, if basically I need a total of 7 balls of yarn to do panels 1 & 3, then panel 2 should take 7 balls of yarn.  I have 16, so I should be good.  While I was doing this math last night and pondering the yarn issue - I took a quick look at panel 1 and saw one cable where I failed to cross it.  Had I crossed it the wrong way, I would have just let it be - let it be a design element.  But I didn't cross it at all.  I didn't like the way it looked.  So, I sucked it up, took those 8 stitches down to the error and have been reknitting.  Notice I didn't tink the whole thing back - just those 8 stitches.  This is the first time I've tried something like that and I am so damn proud of myself!   It's not easy, I'm actually doing a little continental knitting here, only problem is I'm twisting my purl stitches.
So, back to the yarn issue.  I decided this morning that what I would do is stop knitting on panel 1 where I am, put the stitches on some waste yarn.  Then I will knit panel 3 to the same point and put it on waste yarn.  Then I'll do the center panel and see where I stand when that gets to the same point.  And for anyone who is curious, the reason I'm knitting panel 3 before the center panel is that 1 & 3 are identical - just mirror images.  If I find that the I'm not happy with the projected width of the afghan after doing 1 & 3, then I can enlarge the center panel and continue to have the project be symmetrical.